A fistula is an abnormal passage typically between two organs, such as an artery and a vein. An arterio-venous (AV) fistula is a natural or an artificial graft, typically made of ePTFE (expanded PTFE), between a vein and an artery. An AV fistula, as used herein, also includes naturally-occurring native tissue tubular connections between a vein and an artery. AV fistulas are often used to provide multiple needle access sites for hemodialysis. The AV fistula also helps to increase blood flow through the vein to accommodate the flow rate of blood needed for hemodialysis.
One problem associated with AV fistulas is the progressive narrowing of the AV fistula at the junction with the vein. Such obstructions occur when vascular muscle cells begin growing inwardly causing, for example, thrombosis within the AV fistula. When the thrombus becomes sufficiently large, blood flow decreases and the AV fistula ceases to be effective. It has been found that graft patency after six months is only 66% and that graft failure occurs, on the average, after 18 months.
Improved graft patency has been achieved by the use of vascular clips instead of suturing the AV fistula to the vein. Variations in the angle of implantation have also been shown to affect AV fistula patency. The use of a short length of a PTFE graft has been inserted in the vein to improve patency. (A. S. Coulson, et al., A Combination of the Elephant Trunk Anastomosis Technique and Vascular Clips for Dialysis Grafts, Surgical Rounds, 596-608, November 1999.) Also, a PTFE bypass graft to a proximal dilated vein has been used in response to the occurrence of graft-vein stenosis. (Polo, J. R., The State of the Art of Surgical Treatment for Failing Grafts, The Seventh Biannual Symposium on Dialysis Accessxe2x80x94Vascular Access for Hemodialysis VII, pp.8-9, May 2000.) Balloon angioplasty and endovascular stents may be used to treat stenosis in AV fistulas (J. E. Aruny, et al., Quality Improvement Guidelines for Percutaneous Management of the Thrombosed on Dysfunctional Dialysis Access, JVIR, 10:491-498, April 1999.) However, there still exists the need to stop, or at least slow, the obstruction of the AV fistula to prolong the patency of the graft.
The present invention is directed to an AV fistula and a method for enhancing the function of an AV fistula by helping to prevent or at least retard the obstruction of the AV fistula at either or both the arterial and venous sides of the fistula.
A first aspect of the invention is directed to an AV fistula function enhancing method including selecting an endoluminal prosthesis including a coiled body and a graft material covering at least part of the coiled body to create a coiled stent graft The stent graft is placed within the AV fistula and optionally within at least one blood vessel to which the AV fistula is connected. The use of the stent graft helps to prevent, or at least retard, the obstruction of the AV fistula by eliminating, or at least reducing, the accumulation of matter in the AV fistula.
Another aspect of the invention is directed to an AV fistula assembly, including an AV fistula having a tubular body and a coiled stent graft housable at least partially within the AV fistula and at least one of the venous and arterial ends.
The turns of the stent graft at the junction may be spaced apart from one another so to insubstantially or partly hinder fluid flow along the vein. The turns of the stent graft may also be such as to effectively block fluid flow along the vein.
Other features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings.